1. Field of the Invention
The present invention relates to a semiconductor device having an image sensor and, for example, to an image sensor having a light-shielding layer formed from the uppermost metal interconnection layer.
2. Description of the Related Art
In an image sensor, a coating layer is formed under microlenses. This aims at increasing the adhesion between the microlenses and the passivation film of the uppermost layer. A light-shielding layer consisting of the uppermost metal interconnection layer of a metal interconnection multilayer is formed around the pixel area to detect the dark signal level of each pixel.
An image sensor manufacturing method will briefly be described below. An intra-pixel interconnection layer is formed on a semiconductor substrate which has a pixel area with photodiodes. An interlayer dielectric film is formed on the semiconductor substrate with the intra-pixel interconnection layer. Next, the interlayer dielectric film is polished and planarized by, e.g., CMP. A light-shielding layer consisting of the uppermost metal interconnection layer is formed on the semiconductor substrate around the pixel area. A passivation film is formed on the semiconductor substrate having the light-shielding layer. A coating layer is applied to the passivation film. Microlenses are formed on the coating layer in correspondence with pixels arranged in the pixel area.
In a thus manufactured image sensor, however, since the light-shielding layer is continuously formed around the pixel area, the coating layer on the light-shielding layer near the pixel area flows into the pixel area. For this reason, the coating layer in the pixel area thickens at a part close to the light-shielding layer. This phenomenon is called striation. When microlenses are formed in the region with striation, they have uneven heights. This causes color inconsistency in an image generated by the pixels in the pixel area near the light-shielding layer, resulting in a fatal defect for the image sensor.
As a conventional technique related to the present invention, a solid-state image sensing device has been proposed, which thins the interconnection layer and the light-shielding film formed around the effective pixel area, thereby increasing the flatness of the interlayer film and preventing color misregistration (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2002-76322).